What's the difference between a iphone 4 and a iphone 4 cdma?

That has the iphone 4 that does not have the iphone 4 cdma?
its a good idea buy a iphone 4 cdma?
is a good idea pay 50 dollars a a blackberry?
or better buy a ipod with something wrong?

Cdma means it is verizon. Gsm means att.
Blackberry? Heck no.
Ipod- only if it is the newest gen.

Buying the CDMA model depends on the carrier you plan to go with. Verizon (CDMA), AT&T (GSM).

Differences between them
-No SIM slot on CDMA model
-slightly repositioned headphone jack, volume buttons, silent switch

No, don't buy the BlackBerry.